Field of the Invention
The present invention relates to a light emitting device including first and second power sources, a method of controlling the same, an image pickup apparatus, and a storage medium, and more particularly to a method for emitting light without being affected by a charging recycle period or the like.
Description of the Related Art
In recent years, among image pickup apparatuses, such as a digital still camera and a mobile phone with a camera function, with increase in luminance of a light emitting element, such as an LED, an increasing number of them use an LED for a light emitting device (hereinafter also referred to as “the strobe” or “the flash”).
In a flash circuit using an LED, a high-voltage circuit is not required, differently from a flash circuit using a light emitting tube, such as a Xenon tube. Therefore, for the flash circuit using an LED, it is possible to configure an LED drive circuit as a circuit relatively compact in size.
Further, the LED is higher in light emission efficiency than the Xenon tube, and is capable of reducing electric power consumed for obtaining the same amount of light emission by increasing the efficiency of the drive circuit.
However, when performing strobe photographing (flash photographing) of a still image with the flash using an LED (hereinafter referred to as “the LED flash”), although the LED is high in light emission efficiency, it is necessary to cause a large amount of current to instantaneously flow through the LED.
To drive the LED, there has been proposed, for example, a flash unit which is provided with a capacitor having a large capacity, such as an electric double-layer capacitor, as an auxiliary power supply of a battery for the LED flash (LED strobe) (see Japanese Laid-Open Patent Publication No. 2010-4692).
In this flash unit, the electric double-layer capacitor as the auxiliary power source is charged and is used as an input power supply for the LED, whereby a large current is caused to instantaneously flow through the LED to drive the same.
By the way, in an LED drive circuit described in Japanese Laid-Open Patent Publication No. 2010-4692, a recycle time occurs when charging the electric double-layer capacitor from a battery. During this recycle time, the user cannot perform strobe photographing. For example, unless the charging voltage of the electric double-layer capacitor exceeds at least the anode electric potential of the LED, it is impossible to cause the LED to emit light.
Further, when considering so-called full light emission from the LED, it is impossible to perform full light emission from the LED during a charging time period for charging the LED to a charging voltage required to perform full light emission, which is higher than the anode electric potential of the LED.
As described above, in the LED drive circuit described in Japanese Laid-Open Patent Publication No. 2010-4692, the user cannot perform strobe photographing during the charging time period for charging the electric double-layer capacitor, which sometimes prevents the user from immediately performing strobe photographing even when the user desires to perform strobe photographing.